I had a small board I waned to make that has a full ground plane on one side. I printed the toner patterns directly in Eagle, making sure to mirror the top side. The best paper I have found for this is Color Laser Gloss from Hammermill. It is much thinner than photo paper but has the same glossy surface, and is only about $15.00 for 300 sheets.
I cut the patterns in long strips, and trimmed the top pattern so it had about a 1" overhang from the each side of the toner pattern. Then using a strong back-light I aligned the two patterns and taped the top pattern to the bottom. I then stuck a piece of paper in between the two patterns to
protect the bottom pattern while I worked on the top.
Using an eye-dropper I placed a small amount of the solvent on one side of the prepared board blank., and slid it between the patterns. After positioning the blank I applied a few more drops of the solvent on top of the paper and spread it around until I could clearly see the toner pattern through the paper.
When It was positioned where I wanted it I placed a piece of printer paper on top and covered with a piece of blank circuit board. I applied pressure for about a minute to set the toner in position. I then removed the blank board and first with the paper still in place I used the back of a fork to burnish the toner pattern. After a little while the paper began to become more opaque. Then I removed the piece of printer paper and continued the burnishing with medium pressure.
When it looked like all the solvent had evaporated from the paper, I turned it over , removed the piece of paper that had been there to protect the bottom toner pattern. Carefully lifting the pattern slightly I put a few drops of solvent on the board blank and spread it around until even. I added a little more solvent to the top of the paper until I could clearly see the pattern. I processed this side the same way as I had the other.
I checked the board and everything looked fine. I found one or two small pinholes in the toner on the large ground plane area that I touched up with a marker. After etching I drilled a couple of holes in the board to check registration. The photo shows the same hole as seen from both sides of the board. The registration was much better than I had ever been able to get using the hot method with a laminator.